Optical fiber micro-force sensor based on N00N state and demodulation method

Abstract

The invention belongs to the technical field of optical fiber sensing, and discloses an optical fiber micro-force sensor based on an N00N state and a demodulation method. The N00N-state light source outputs two beams of path entangled light, and the two beams firstly enter a first port of the optical fiber circulator through the three-core optical fiber, are output from a second port and enter the micro-force probe through transmission of the three-core optical fiber. One light beam is reflected on one end face of the optical fiber Fabry-Perot interferometer microcavity, and the other light beam is reflected on the other end face of the optical fiber Fabry-Perot interferometer microcavity. Reflected light enters the fiber core to be propagated and generate interference, and interference light enters the fiber core from the second port and is output from the third port, passes through the optical fiber coupler and then enters the photoelectric detector for coincidence counting. When the force-sensitive material is subjected to micro force, the length of the interferometer is changed, and the interference light intensity is changed. The micro-force variation can be calculated by measuring the coincidence count value.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber micro-force sensor based on a N00N state and a demodulation method. Background Art

[0002] Microforce measurement refers to the technology used to measure extremely small forces, typically in the nanonewton or even piconewton range. Microforce measurement primarily involves optical and electromagnetic methods. Optical methods include interferometers, atomic force microscopes, and optical tweezers. Electromagnetic methods primarily include piezoelectric elements and capacitive sensors. Microforce measurement holds broad application prospects, including measuring the mechanical properties of cells, protein folding, and the mechanical properties of nanomaterials.

[0003] The N00N state is a quantum entangled state capable of transcending the shot noise limit, theoretically reaching the Heisenberg limit. This makes it useful for measuring tiny changes in physical quantities. N00N states can typically be generated through spontaneous parametric conversion in nonlinear crystals or spontaneous four-wave mixing in optical fibers. Sensing measurements typically use N00N states with N=1 and 2. By inputting the N00N state into an interferometer, its phase information can be obtained through population count detection, allowing calculation of the change in the physical quantity.

[0004] The Fabry-Perot interferometer is a high-precision optical device based on multi-beam interference. Its core consists of two parallel, highly reflective mirrors forming an optical resonant cavity. Fiber-optic Fabry-Perot sensors offer advantages such as simple structure, compact size, high sensitivity, excellent stability, and immunity to electromagnetic interference. Therefore, they are widely used in measurement of strain, temperature, and pressure. An incident light beam interferes in a Fabry-Perot interferometer. As the cavity length changes, the intensity of the interfering light also changes. By detecting changes in the intensity of the interfering light, the change in the desired measurement can be inferred.

[0005] Most existing micro-force measurement systems do not use quantum technology, which limits their detection limits and sensitivity. A stress measurement device based on a fiber-optic Fabry-Perot interferometer (FPI) is currently available. The light source used is an amplified spontaneous emission light source, which generates interference light through a fiber-optic Fabry-Perot interferometer. A strain gauge acts on one end of the optical fiber to cause the interferometer to deform. The stress can be demodulated by measuring the changes in the interference spectrum using a spectrometer. The spectrometer has a resolution of 5mN, which is sufficient for measuring macroscopic micro-forces. Microscopic forces, such as those occurring between cells and biomacromolecules, cannot be detected by fiber-optic sensors using ordinary light sources. Using a quantum light source and a FPI can sense and measure micro-forces through quantum state interference, which is of great significance for further improving the micro-force sensing limit. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose an optical fiber micro-force sensor based on the N00N state and a demodulation method.

[0007] The technical solution of the present invention is as follows: an optical fiber micro-force sensor based on N00N state, comprising a N00N state source, an optical fiber, an optical fiber circulator, a micro-force probe, an optical fiber coupler and a photodetector;

[0008] The optical fibers include a first optical fiber, a second optical fiber, a third optical fiber, and a fourth optical fiber; the first optical fiber and the second optical fiber are both triple-core optical fibers;

[0009] The N00N state source generates two beams of path-entangled state light, namely the first beam and the second beam;

[0010] The first light beam generated by the N00N state source propagates through the core a of the first optical fiber, and the second light beam propagates through the core c of the first optical fiber; the first light beam and the second light beam are incident on the first port of the optical fiber circulator through the first optical fiber, and then exit from the second port of the optical fiber circulator and enter the second optical fiber; the first light beam propagates along the core a of the second optical fiber, and the second light beam propagates along the core c of the second optical fiber; after leaving the second optical fiber, the first light beam and the second light beam enter the micro-force probe and propagate along the waveguides in the micro-force probe;

[0011] The micro-force probe includes a single-mode optical fiber, a waveguide a, a waveguide b, an optical fiber Fabry-Perot interferometer, and a force-sensitive material; wherein the waveguide a, the waveguide b, and the core of the single-mode optical fiber are located in the same plane, and the waveguide a and the waveguide b are located on both sides of the core; the waveguide a is not connected to the optical fiber Fabry-Perot interferometer, and the waveguide b is connected to the optical fiber Fabry-Perot interferometer; the force-sensitive material is located at one end of the optical fiber Fabry-Perot interferometer;

[0012] The first light beam propagates along waveguide a, and the second light beam propagates along waveguide b. After emitting from waveguide a, the first light beam is reflected at the first end face of the optical fiber Fabry-Perot interferometer. After emitting from waveguide b, the second light beam is reflected at the second end face of the optical fiber Fabry-Perot interferometer. The two reflected light beams are incident on the core of the single-mode optical fiber and interfere with each other, forming interference light that enters the core b of the second optical fiber and propagates. After entering the second port of the optical fiber circulator, it is output from the third port of the optical fiber circulator and enters the optical fiber coupler along the third optical fiber. After exiting the optical fiber coupler, the interference light is split into two light beams and enters two fourth optical fibers. The interference light is then fed into a coincidence counter by a photodetector for coincidence counting.

[0013] The micro-force acting on the force-sensitive material changes the cavity length of the fiber Fabry-Perot interferometer, causing the phase information of the interference light to change, and then changing the coincidence count value; by demodulating the coincidence count value, the size of the micro-force to be measured is measured.

[0014] The two beams of path entangled state light are and ,in is a positive integer; the number of N00N states output by the N00N state source per second is greater than 10,000.

[0015] The third optical fiber is a single-mode optical fiber.

[0016] The fourth optical fiber is a single-mode optical fiber.

[0017] The waveguide a and waveguide b are obtained by etching in a single-mode optical fiber by a femtosecond laser, and the medium is air; the starting points of both waveguide a and waveguide b are the single-mode optical fiber cladding, and the arrangement angle of waveguide a and waveguide b ensures that the reflected light enters the fiber core.

[0018] The optical fiber Fabry-Perot interferometer is a hollow optical fiber, the core medium of the hollow optical fiber is air, and is fused with a single-mode optical fiber.

[0019] The initial cavity length of the optical fiber Fabry-Perot interferometer ensures that the reflected light of the first light beam and the reflected light of the second light beam have a phase difference of 90 degrees.

[0020] The optical fiber coupler is a single-mode optical fiber with a splitting ratio of 50:50.

[0021] A coincidence counter counts the photons that arrive at two photodetectors simultaneously.

[0022] A demodulation method of optical fiber micro-force sensor based on N00N state. When acting on a force-sensitive material, the length change of the fiber Fabry-Perot interferometer is:

[0023] ;

[0024] is the stiffness of the fiber Fabry-Perot interferometer;

[0025] The interference phase change caused by the change of the cavity length of the fiber Fabry-Perot interferometer is: , and eventually causes the output N00N state to change;

[0026] According to the basic theory of fiber Fabry-Perot interferometer, the relationship between micro-force and interference phase change is obtained:

[0027] ;

[0028] is the wavelength of the N00N state;

[0029] For the two-photon N00N state, the probability distribution function of the output photon is,

[0030] ;

[0031] is the phase information of the N00N state;

[0032] The change in the probability of output photons is obtained as follows:

[0033] ;

[0034] The reflectivity of the micro-force probe is used for demodulation. The reflectivity of the micro-force probe is defined as:

[0035] ;

[0036] in, is the number of N00N states detected by the fiber Fabry-Perot interferometer reflection, is the number of N00N states input to the fiber Fabry-Perot interferometer;

[0037] The change in the output photon probability causes the photodetector to count the change , the corresponding reflectivity changes to ;

[0038] Finally, the cavity length change of the fiber Fabry-Perot interferometer is obtained as follows:

[0039] ;

[0040] The measured micro-force is,

[0041] .

[0042] Beneficial effects of the present invention: Through theoretical calculations, it can be concluded that the resolution of micro-force measurement of the optical fiber micro-force sensor based on the N00N state can reach 0.477pN, which can meet the measurement of the bonding force (pN level) in the process of T cell receptor binding to antigen, and can be applied to the study of microscopic biological interaction mechanisms. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the structure of the optical fiber micro-force sensor based on the N00N state.

[0044] Figure 2 This is a schematic diagram of the structure of the micro-force probe of the optical fiber micro-force sensor based on the N00N state.

[0045] Figure 3 It is a schematic diagram of the cross section of a three-core optical fiber.

[0046] In the figure: 1-N00N state source; 101-first light beam; 102-second light beam; 103-interference light; 104-light; 2-first optical fiber; 3-optical fiber circulator; 301-first port; 302-second port; 303-third port; 4-second optical fiber; 401-fiber core a; 402-fiber core b; 403-fiber core c; 5-micro-force probe; 501-single-mode optical fiber; 502-waveguide a; 503-waveguide b; 504-fiber core; 505-fiber Fabry-Perot interferometer; 506-hollow-core optical fiber; 507-first end face; 508-second end face; 509-force-sensitive material; 6-third optical fiber; 7-optical fiber coupler; 8-photodetector; 9-fourth optical fiber; 10-coincidence counter; 11-micro-force. DETAILED DESCRIPTION

[0047] An optical fiber micro-force sensor based on N00N state, comprising a N00N state source 1, an optical fiber, an optical fiber circulator 3, a micro-force probe 5, an optical fiber coupler 7 and a photodetector 8;

[0048] The optical fiber includes a first optical fiber 2, a second optical fiber 4, a third optical fiber 6, and a fourth optical fiber 9. Both the first optical fiber 2 and the second optical fiber 4 are triple-core optical fibers. If single-mode optical fiber single-core transmission is used, the N00N state path entanglement characteristic disappears. The cores of the first optical fiber 2 and the second optical fiber 4 include core a401, core b402, and core c403, respectively.

[0049] The N00N state source 1 generates two beams of path entangled state light, namely a first beam 101 and a second beam 102;

[0050] The first light beam 101 generated by the N00N state source 1 propagates through the core a401 in the first optical fiber 2, and the second light beam 102 propagates through the core c403 in the first optical fiber 2; the first light beam 101 and the second light beam 102 are incident on the first port 301 of the optical fiber circulator 3 through the first optical fiber 2, and enter the second optical fiber 4 after being emitted from the second port 302 of the optical fiber circulator 3; the first light beam 101 propagates along the core a401 of the second optical fiber 4, and the second light beam 102 propagates along the core c403 of the second optical fiber 4; after leaving the second optical fiber 4, the first light beam 101 and the second light beam 102 enter the micro-force probe 5 and propagate along the waveguides in the micro-force probe 5;

[0051] Because the waveguide a502, waveguide b503 and fiber core 504 of the micro-force probe 5 are a total of three optical paths, the first optical fiber 2 needs to be set up with three cores, and because the waveguide a502 and waveguide b503 are located on both sides of the fiber core 504, the first light beam 101 and the second light beam 102 pass through the fiber cores at both ends.

[0052] The micro-force probe 5 includes a single-mode optical fiber 501, a waveguide a502, a waveguide b503, an optical fiber Fabry-Perot interferometer 505, and a force-sensitive material 509; wherein the waveguide a502, the waveguide b503, and the core 504 of the single-mode optical fiber 501 are located in the same plane, and the waveguide a502 and the waveguide b503 are located on both sides of the core 504;

[0053] The first light beam 101 propagates along waveguide a502, and the second light beam 102 propagates along waveguide b503; waveguide a502 is not connected to the optical fiber Fabry-Perot interferometer 505, and waveguide b503 is connected to the optical fiber Fabry-Perot interferometer 505; during etching, waveguide a502 and the optical fiber Fabry-Perot interferometer 505 are not connected, and reflection occurs due to the difference in refractive index. After the first light beam 101 is emitted from waveguide a502, it is reflected at the first end face 507 of the optical fiber Fabry-Perot interferometer. After the second light beam 102 is emitted from waveguide b503, it is reflected at the second end face 508 of the optical fiber Fabry-Perot interferometer. After being reflected at the second end face 508 of the optical fiber Fabry-Perot interferometer, the second light beam 102 enters the fiber core 504, and a part of it will also be reflected at the first end face 507 of the optical fiber Fabry-Perot interferometer. The interference generated at the first end face 507 of the optical fiber Fabry-Perot interferometer will not affect the symbol Total count; After the two reflected light beams are incident on the core 504 of the single-mode optical fiber 501 and interfere with each other, the interference light is generated and enters the core b402 of the second optical fiber 4. After being incident on the second port 302 of the optical fiber circulator 3, it is output from the third port 303 of the optical fiber circulator 3 and enters the optical fiber coupler 7 along the third optical fiber 6. After being output from the optical fiber coupler 7, the interference light is split into two light beams 104 and enters the fourth optical fiber 9. The two light beams 104 are composed of a plurality of single photons and enter the coincidence counter 10 by the photodetector 8 for coincidence counting.

[0054] The micro-force 11 acts on the force-sensitive material 509 to change the cavity length of the optical fiber Fabry-Perot interferometer 505, causing the phase information of the interference light 103 to change, and then changing the coincidence count value; by demodulating the coincidence count value, the size of the micro-force to be measured is measured.

[0055] The two beams of path entangled state light are and ,in is a positive integer; the number of N00N states output by N00N state source 1 per second is greater than 10,000.

[0056] The third optical fiber 6 is a single-mode optical fiber.

[0057] The fourth optical fiber 9 is a single-mode optical fiber.

[0058] The waveguide a502 and waveguide b503 are obtained by etching in the single-mode optical fiber 501 by femtosecond laser, and the medium is air; the starting points of both waveguide a502 and waveguide b503 are the single-mode optical fiber cladding, and the arrangement angle of waveguide a502 and waveguide b503 ensures that the reflected light enters the fiber core 504.

[0059] The optical fiber Fabry-Perot interferometer 505 is a hollow-core optical fiber 506 , the core medium of the hollow-core optical fiber 506 is air, and is fused with the single-mode optical fiber 501 .

[0060] The initial cavity length of the optical fiber Fabry-Perot interferometer 505 ensures that the reflected light of the first light beam 101 and the reflected light of the second light beam 102 have a phase difference of 90 degrees.

[0061] The optical fiber coupler 7 is a single-mode optical fiber with a splitting ratio of 50:50.

[0062] The coincidence counter 10 counts the photons that arrive at the two photodetectors 8 simultaneously.

[0063] A demodulation method of optical fiber micro-force sensor based on N00N state. When 11 acts on the force-sensitive material 509, the length change of the fiber Fabry-Perot interferometer 505 is:

[0064] ;

[0065] is the stiffness of the fiber Fabry-Perot interferometer 505;

[0066] The interference phase change caused by the change of the cavity length of the fiber Fabry-Perot interferometer 505 is: , and eventually causes the output N00N state to change;

[0067] According to the basic theory of fiber Fabry-Perot interferometer, the relationship between micro-force and interference phase change is obtained:

[0068] ;

[0069] is the wavelength of the N00N state;

[0070] For the two-photon N00N state, the probability distribution function of the output photon is,

[0071] ;

[0072] is the phase information of the N00N state;

[0073] The change in the probability of output photons is obtained as follows:

[0074] ;

[0075] Demodulation is performed using the reflectivity of the micro-force probe 5, which is defined as:

[0076] ;

[0077] in, is the number of N00N states detected by the fiber Fabry-Perot interferometer reflection, is the number of N00N states input to the fiber Fabry-Perot interferometer;

[0078] The change in the output photon probability causes the photodetector 8 to count the change in the amount , the corresponding reflectivity changes to ;

[0079] Finally, the cavity length change of the fiber Fabry-Perot interferometer is obtained as follows:

[0080] ;

[0081] The measured micro-force is,

[0082] .

[0083] when When , the measured micro-force is,

[0084] .

[0085] Furthermore, waveguide a 502 and waveguide b 503 are etched in single-mode optical fiber 501 by a femtosecond laser. The medium inside waveguide a 502 and waveguide b 503 is air. Both waveguides originate from the single-mode optical fiber cladding and are angled so that reflected light enters the fiber core 504.

[0086] Furthermore, the force-sensitive material 509 has a reflectivity of more than 95%.

[0087] The coincidence counter 10 counts the photons that arrive at the two photodetectors 8 simultaneously.

[0088] The demodulation method is given by the functional relationship between the micro-force size and the number of photon coincidence counts.

[0089] When the minimum number of N00N states detectable by the optical fiber micro-force sensor based on N00N state is 1, the photon wavelength , , , When the minimum micro-force value can be measured is This theoretical measurement limit exceeds the limit of existing atomic force microscopes. .

[0090] The present invention will be further described below with reference to specific embodiments.

[0091] The binding process between T cell receptor and antigen involves bonding force, which is in the order of pN and cannot be measured using ordinary fiber optic sensors. The N00N state with N=2 is selected as the N00N state source 1 and input to the first optical fiber 2. The surface of the force-sensitive material 509 of the micro-force probe 5 is modified with antigen and placed in a T cell solution. When the receptor binds to the antigen, a bonding force is generated. The combining and separating processes will cause the cavity length of the optical fiber Fabry-Perot interferometer 505 to change, which in turn affects the phase information of the first light beam 101 and the second light beam 102, causing the coincidence count value to change.

[0092] Record the change in the coincidence count when the receptor binds and dissociates , according to the demodulation scheme, the theoretically measurable minimum bonding force is , which can meet the detection needs of the process of T cell receptor binding to antigen.

Claims

1. An optical fiber micro-force sensor based on N00N state, characterized in that: The optical fiber micro-force sensor based on the N00N state comprises a N00N state source (1), an optical fiber, an optical fiber circulator (3), a micro-force probe (5), an optical fiber coupler (7) and a photodetector (8); The optical fibers include a first optical fiber (2), a second optical fiber (4), a third optical fiber (6) and a fourth optical fiber (9); the first optical fiber (2) and the second optical fiber (4) are both three-core optical fibers; The N00N state source (1) generates two beams of path-entangled state light, namely a first beam (101) and a second beam (102); The first light beam (101) generated by the N00N state source (1) propagates through the core a (401) in the first optical fiber (2), and the second light beam (102) propagates through the core c (403) in the first optical fiber (2); the first light beam (101) and the second light beam (102) are incident on the first port (301) of the optical fiber circulator (3) through the first optical fiber (2), and then exit from the second port (302) of the optical fiber circulator (3) and enter the second optical fiber (4); the first light beam (101) propagates along the core a (401) of the second optical fiber (4), and the second light beam (102) propagates along the core c (403) of the second optical fiber (4); after leaving the second optical fiber (4), the first light beam (101) and the second light beam (102) enter the micro-force probe (5) and propagate along the waveguides in the micro-force probe (5); The micro-force probe (5) comprises a single-mode optical fiber (501), a waveguide a (502), a waveguide b (503), an optical fiber Fabry-Perot interferometer (505) and a force-sensitive material (509); wherein the waveguide a (502), the waveguide b (503) and the core (504) of the single-mode optical fiber (501) are located in the same plane, and the waveguide a (502) and the waveguide b (503) are located on both sides of the core (504); the waveguide a (502) is not connected to the optical fiber Fabry-Perot interferometer (505), and the waveguide b (503) is connected to the optical fiber Fabry-Perot interferometer (505); the force-sensitive material (509) is located at one end of the optical fiber Fabry-Perot interferometer (505); The first light beam (101) propagates along the waveguide a (502), and the second light beam (102) propagates along the waveguide b (503); after the first light beam (101) is emitted from the waveguide a (502), it is reflected at the first end face (507) of the optical fiber Fabry-Perot interferometer; after the second light beam (102) is emitted from the waveguide b (503), it is reflected at the second end face (508) of the optical fiber Fabry-Perot interferometer; the two reflected light beams are incident on the core (504) of the single-mode optical fiber (501) and generate After the interference, the interference light enters the core b (402) of the second optical fiber (4) and propagates, is incident from the second port (302) of the optical fiber circulator (3), is output from the third port (303) of the optical fiber circulator (3), and enters the optical fiber coupler (7) along the third optical fiber (6); after being output from the optical fiber coupler (7), the interference light is divided into two beams of light (104) and respectively enters the two fourth optical fibers (9), and enters the coincidence counter (10) through the photoelectric detector (8) for coincidence counting; The micro-force (11) acts on the force-sensitive material (509) to change the cavity length of the optical fiber Fabry-Perot interferometer (505), causing the phase information of the interference light (103) to change, thereby changing the coincidence count value; by demodulating the coincidence count value, the magnitude of the micro-force to be measured is measured.

2. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The two beams of path entangled state light are and ,in is a positive integer; the number of N00N states output by the N00N state source (1) per second is greater than 10,000.

3. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The third optical fiber (6) is a single-mode optical fiber.

4. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The fourth optical fiber (9) is a single-mode optical fiber.

5. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The waveguide a (502) and the waveguide b (503) are obtained by etching a femtosecond laser in a single-mode optical fiber (501), and the medium is air; the starting points of both the waveguide a (502) and the waveguide b (503) are the single-mode optical fiber cladding, and the arrangement angles of the waveguide a (502) and the waveguide b (503) ensure that the reflected light enters the fiber core (504).

6. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The optical fiber Fabry-Perot interferometer (505) is a hollow optical fiber, the core medium of the hollow optical fiber is air, and is fused with the single-mode optical fiber (501).

7. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The initial cavity length of the optical fiber Fabry-Perot interferometer (505) ensures that the reflected light of the first light beam (101) and the reflected light of the second light beam (102) have a phase difference of 90 degrees.

8. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The optical fiber coupler (7) is a single-mode optical fiber with a splitting ratio of 50:

50.

9. The optical fiber micro-force sensor based on the N00N state according to claim 1, characterized in that: The coincidence counter (10) counts the photons that arrive at the two photodetectors (8) simultaneously.

10. A demodulation method for an optical fiber micro-force sensor based on a N00N state according to any one of claims 1 to 9, characterized in that: Dangweili (11) When acting on the force-sensitive material (509), the length of the fiber Fabry-Perot interferometer (505) changes to: ； is the stiffness of the fiber Fabry-Perot interferometer (505); The change in the interference phase caused by the change in the cavity length of the fiber Fabry-Perot interferometer (505) is: , and eventually causes the output N00N state to change; According to the basic theory of fiber Fabry-Perot interferometer, the relationship between micro-force and interference phase change is obtained: ； is the wavelength of the N00N state; For the two-photon N00N state, the probability distribution function of the output photon is, ； is the phase information of the N00N state; The change in the probability of output photons is obtained as follows: ； The reflectivity of the micro-force probe (5) is used for demodulation. The reflectivity of the micro-force probe (5) is defined as, ； in, is the number of N00N states detected by the fiber Fabry-Perot interferometer reflection, is the number of N00N states input to the fiber Fabry-Perot interferometer; The change in the output photon probability causes the photodetector (8) to count the change in the amount of , the corresponding reflectivity changes to ; Finally, the cavity length change of the fiber Fabry-Perot interferometer is obtained as follows: ； The measured micro-force is, 。

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